Spool valves are well-known in the art for controlling hydraulic systems. As shown in FIGS. 1a and 1b, a typical spool valve 1 comprises a spool housing 2 having a spool cavity 3 defined by an inner surface 2a of the housing 2, and a spool 4 disposed within the spool cavity 3 having a plurality of lands 5 separated by a plurality of grooves 6. The spool 4 is moveable along its longitudinal axis L in response to actuation of the spool valve 1, and the lands 5 are in sliding contact with the inner surface 2a of the housing 2. The spool valve 1 further comprises a control port 7 passing through the inner surface 2a of the housing 2 in fluid communication with the spool cavity 3. A chamber 8 is defined between the groove 6, the land 5 and the inner surface 2a of the housing 2. The lands 5 have radially extending metering edges 9 (as are well-known in the art of spool valves) which permit or prevent fluid communication between the control port 7 and the chamber 8 depending on the longitudinal position of the spool 4 within the spool cavity 3. As shown in FIG. 1a, the metering edges 9 are radially aligned with the edges of the control port 7, so no fluid communication is permitted between the control port 7 and the chamber 8. As shown in FIG. 1b, actuation of the spool valve 1 causing the spool 4 to move longitudinally (to the right as you look at the Figure) causing the metering edges 9 to become radially misaligned with the edges of the control port 7, which permits fluid communication between the control port 7 and the chamber 8. In this manner, actuation of the spool valve 1 can be used to control fluid movement in a hydraulic system, such as a servovalve.
As shown in FIG. 1b, in typical spool valves 1, high fluid pressure in the housing 2 and control ports 7 can cause deformation of the housing 2 adjacent the control port 7. Deformed portions 2b of the housing 2 can lock the spool 4 in a longitudinal position and/or prevent it from moving back to another longitudinal position. Since the radial clearance between the spool 4 and housing 2 is typically in the micrometer range, any small deformation could lock the spool 4. Spool locking prevents proper function of the spool valve and associated hydraulic system, and may result in having to replace the spool valve.
The present disclosure aims to provide a spool that prevents the aforementioned spool housing deformation.